High selectivity process for vapor phase oxydehydrogenation of alkanoic acids, such as isobutyric acid, using Dawson structure phosphomolybdic acid

Abstract

A novel method of converting alkanoic acids, such as isobutyric acid, to alpha-beta unsaturated acids, such as methacrylic acid, is disclosed which exhibits a higher degree of selectivity than those vapor phase oxydehydration methods heretofore known to the art. The preferred method comprises contacting a Dawson structure phosphomolybdic acid catalyst with isobutyric acid under specified reaction conditions to achieve a high selectivity for methacrylic acid.

We claim: 
     
       1. A method for producing an alpha-beta unsaturated acid, comprising the steps of: (a) providing an alkanoic acid having at least one hydrogen atom attached to each of the alpha and beta carbons thereof;   (b) providing a catalyst comprising a Dawson cluster phosphomolybdic acid;   (c) contacting said catalyst at a temperature between 260° C. and the temperature at which substantial decomposition of said catalyst occurs with a reaction gas comprising said alkanoic acid, water and oxygen to convert at least a portion of said alkanoic acid into a reaction product comprising its corresponding alpha-beta unsaturated alkanoic acid.   
     
     
       2. The method of claim 1 wherein said alkanoic acid of step (a) is isobutyric acid. 
     
     
       3. The method of claim 1 wherein said reaction gas comprises an inert diluent gas. 
     
     
       4. The method of claim 1 wherein said method is performed at temperature between 260° and 330° C. 
     
     
       5. The method of claim 4 wherein said method is performed at about 280° C. 
     
     
       6. The process of claim 2 wherein said catalyst is deposited on a substrate, as carrier. 
     
     
       7. The method of claim 6 wherein said substrate is silica.